To prepare a patient for open heart surgery, blood flowing to the patient's heart is diverted to a heart and lung machine that mechanically performs the functions of the heart and lungs during the surgical procedure. Thus deprived of its usual supply of oxygenated blood, heart muscle begins to deteriorate. Accordingly, recognizing the preservative effects of refrigeration, physicians began the practice of placing ice packs around the heart during surgery. The use of ice packs does produce some beneficial effect, but such use is somewhat unsatisfactory due to the physical limitations of ice packs. More particularly, they can not be positioned easily under the heart of a supine patient, they do not contact all of the walls of the heart and thus create warm pockets where muscle deterioration is not adequately curtailed, and they melt and require replacement which interferes with the physician's work. Moreover, the melted ice collects in a puddle below the heart, in the thoracic cavity, thereby affecting the lungs and possibly precipitating the onset of pulmonary problems or other complications; even the removal of such puddles during surgery creates an additional set of problems. Ice packs are also bulky and thus limit the surgeon's freedom of movement. Perhaps even more significantly, the ice packs cool everything with which they come into contact, i.e., they cool the thoracic cavity and thus the body in general, i.e., the cooling effect provided by ice packs is not localized. Surgical personnel who have worked with ice packs during surgery could point out even more drawbacks.
The heart of a supine patient is supported primarily by the walls of the thoracic cavity, and such walls are at normal body temperature. Thus, the very place where ice packs are least effective is the very place where heart cooling is most needed. There is a need, therefore, for a device that can be easily slipped under the heart of a supine patient to isolate the heart from the walls of the thoracic cavity. There is a need, further, for a device that cools the heart evenly, i.e., in the absence of pockets of uncooled areas. Moreover, there is a need for a device that removes any puddles of coolant that may collect in the thoracic cavity if such puddles become too large and threaten to overly cool said cavity and hence the patient's lungs. The needed device should be easy to manipulate and easy to operate as well.
A number of inventors have tried to develop the needed device, and some of the resulting surgical tools represent improvements over the ice pack method.
For example, U.S. Pat. No. 4,259,961 to Hood shows a plastic cooling is placed under the heart, but the device is structurally complex and difficult to maneuver during surgery. Additional U.S. patents of interest, all of which, like Hood, advanced the art to which they pertained, include U.S. Pat. Nos. 4,154,245 to Daily, 4,971,056 to Seacord, 4,416,281 to Cooper et. al., and 4,327,733 to Gallie. British patent 2,040,169, may also be of interest.
When the respective disclosures of these patents and many others are studied, together with the vast non-patent literature on the subject of heart refrigeration or myocardial hypothermia during surgery, those of ordinary skill in the industry that supplies tools to the medical profession are left with the firm conviction that the art has reached its highest level of development and that further significant progress in this field is unlikely.